"It becomes ridiculous after a while," he tells Parade about what runs though his head when he has to get intimate with Stewart.

"I think the more comfortable you are with each other, the harder it gets to do any kind of really intense relationship scene. You're kind of thinking, 'I don't want to embarrass myself in front of this person.' "

Pattinson, 25, who's been dating his Breaking Dawn – Part 1 costar, 21, for several years, acknowledges the awkwardness, saying, "Watching other people have sex is never going to be that spectacular anyway. It's a strange thing when there's so much hype about it. You are like, 'God, I hope this lives up to it.' "

In fact, the scenes in question actually had to be reshot so as to avoid a R rating by the MPAA, which would limit its audience. (The movie, rated PG-13, opens in theaters Nov. 18.)

"The toughest part was avoiding an R-rating," Pattinson says. "It's funny when people talk about the sex scenes in the book because there are no sex scenes in the book. Go back and read. They always fade to black."